As process technology has scaled, it has become increasingly difficult to control the variation of transistor parameters because of a variety of factors, including, for example, Random Dopant Fluctuation (RDF). Other reasons for this variation include dopant scattering effect, such as the well proximity effect, that makes the placement of dopants in MOSFET transistors increasingly difficult as transistor size is reduced. Misplaced dopants can reduce transistor performance, increase transistor variability, including variability of channel transconductance, capacitance effects, threshold voltage, and leakage. Such variability increases as transistors are reduced in size, with each misplaced dopant atom having a greater relative effect on transistor properties, as a result of the overall reduction in the number of dopant atoms.
Many integrated circuit (IC) devices use a variety of cells that perform specific functions. IC devices can include logic, memory, controller and other functional blocks. Semiconductor IC devices are fabricated in a semiconductor process, often using a complementary metal-oxide-semiconductor (CMOS) process. Transistors are formed in a semiconductor substrate, and usually involve a sequence of fabrication steps that result in a gate with adjacent source and drain, the source and drain being formed in a channel. Typically, an IC device can include different transistor device types including p-channel MOS (PMOS) transistors, n-channel MOS (NMOS) transistors, MOS field effect transistors (MOSFETs) tailored for digital or analog applications, high-voltage MOSFETs, high/normal/low frequency MOSFETs, MOSFETs optimized to work at distinct voltages or voltage ranges, low/high power MOSFETs, and low, regular, or high threshold voltage (Vt) transistors (i.e., low Vt (LVT), standard Vt (SVT), or high Vt (HVT)), etc. Transistor device types are usually distinguished by electrical performance characteristics (e.g., threshold voltage, speed, mobility, transconductance, linearity, noise, power), which can in turn lend themselves to be suitable for a particular application (e.g., signal processing, or data storage). Therefore, a complex IC device such as, for instance, a system on a chip (SoC), can use different transistor types (or a combination of one or more different transistor types) to achieve the target performance for different circuit blocks in the IC device.
The electrical performance characteristics of the different transistor device types in a SoC can be subject to variation due to manufacturing process variations, also referred to as the “manufacturing corner” of a particular transistor device. Typically, the electrical performance variation of the different transistor device types of the SoC can be different because the performance of each transistor device type is impacted differently by the manufacturing process variations.